Interpretive Summary: Eucalyptus plantations in Brazil are rapid expanding in area for fuel and fiber production. Many of these plantations are on slopes in areas with high rainfall intensity. Soil aggregated stability is very important in explaining the erosion potential of these soils. Traditional aggregate size techniques using dry aggregates give conflicting results related to soil erodibility. In order to look at how Eucalyptus farming either reduces or increases the threat of soil to erosion we used a new aggregate stability technique with moist aggregates called the High Energy Moisture Characteristic (HEMC) to measure differences between a natural forested soil and those farmed under Eucalyptus and related it to soil properties at three regions in Brazil. Chemical, physical and mineralogical properties and soil organic matter did not explain differences in observed aggregate stability. All soils were found to have a high stability and therefore Eucalyptus farming did not significantly increase the threat of causing greater soil erosion. Although our aggregate stability results did not show impact from Eucalyptus farming, any soil disturbance during plantation establishment and harvest may still pose a great potential for soil erosion. Soil conservation practices should be implemented during such critical times.

Technical Abstract:
Eucalyptus cultivation has increased in many Brazilian regions. In order to recommend good management practices, it is necessary to understand changes in soil properties where eucalyptus is planted. Aggregate stability analyses have proved to be a useful tool to measure soil effects caused by changes in management practices.Thus, the objectives of this study were to determine the main chemical, physical and mineralogical properties for different soil classes, and assess the relationship between aggregate stability and changes in soil properties under eucalyptus plantation. We studied representative soils within three eucalyptus cultivated regions. Physical, chemical, and mineralogical analyses were performed using standard techniques. Aggregate stability was measured using the high-energy moisture characteristic (HEMC) technique. X-ray diffraction patterns showed that kaolinite was the predominant crystalline clay mineral for all soils, whereas, a small amount of hydroxy-interlayered vermiculite was found in some profiles. Aggregate stability ratio was high and greater than 50% for all soils. This fact shows, for weathered soils with 1:1 clay minerals and Al- and Fe-oxides, that the aggregate stability index is high. In these soils, the stability ratio did not have a good relationship with clay or soil organic matter contents, therefore, the high stability was due to other properties and care should be taken when establishing new plantations or during harvesting.